This invention relates to planar antennas and, more particularly, to a planar antenna capable of receiving circularly polarized waves at a high gain over a wide band.
The planar antennas of the kind referred to are effectively utilized in receiving the circularly polarized waves transmitted as carried on SHF band, in particular, above 12 GHz band from a geostationary broadcasting satellite launched into cosmic space to be 36,000 Km alone from the earth.
1. Field of the Invention
Parabolic antennas erected on the roof or the like positions of house buildings have been generally widely utilized as the antenna for receiving the circularly polarized waves from the geostationary satellite, but parabolic antennas have been defective in that they are susceptible to strong wind and easily fall down due to their bulky three dimensional structure so that additional means for stably supporting them will have to be employed, and that such supporting means further requires high mounting costs and still troublesome installation labor.
2. Description of the Related Art
In attempt to eliminate these problems of the known parabolic antennas, there has been suggested in Japanese Patent Application Laid-Open publication No. 99803/1978 (or corresponding U.S. Pat. No. 4,475,107 or German Offenlegungsschrift No. P 314900.2) a planar antenna which is flattened in the entire configuration, according to which the structure can be much simplified and it is made possible to directly mount the antenna on an outdoor wall or the like position of house buildings so as to be made inexpensive.
Further, the planar antenna has been demanded to be of a high gain, for which purpose various attempts have been made to reduce insertion loss. Disclosed in, for example, U.S. Pat. No. 4,851,855 of the present inventors, K. Tsukamoto et al. (to which U.K. Patent No. 2,187,333, German Patent Application P 37 06 051.1 and French Patent Application No. 87 02421 correspond) prior to the present invention is a planar antenna in which the power supply circuit and the radiation circuit are not connected directly to each other but are electromagnetically coupled for supplying a power from the power supply circuit to the radiation circuit, while both circuits as well as a grounding conductor are respectively carried on each of insulating plates which are separated from one another by means of a space retaining means. With this arrangement, the power supply circuit can be also disposed in the space thus retained, and the insertion loss can be effectively reduced.
Further, prior to the present invention, there has been suggested in U.S. Pat. No. 4,816,835 of T. Abiko et al. (to which U.K. Patent Application No. 87 19750, German Patent Application P 37 29 750 and French Patent Application No. 87 12274 correspond) another planar antenna in which a radiation circuit is provided with many slots in which each of the patch elements is disposed, and such radiation circuit is electromagnetically coupled at the patch elements in the slots to opposed power supply terminals of a power supply circuit, so as to further decrease the insertion loss while incrementally improving the assembling ability.
According to these U.S. Pat. Nos. 4,851,855 and 4,816,835, it is possible to reduce the insertion loss of the planar antennas and to improve them in the assembling ability in contrast to any known planar antennas. In these patents, however, the radiation circuit comprises slots of a square, circular or other shape and patch elements respectively disposed in each of the slots in the form of a floating island so that a highly precise etching process will be required therefor with required etching pattern of the radiation plate made much complicated, and there have arisen such problems that manufacturing fluctuation becomes large to lower the yield or resultant products and required manufacturing costs are generally elevated.